RATIONALE: Drugs used in chemotherapy work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill cancer cells. Peripheral stem cell transplant may allow the doctor to give higher doses of chemotherapy drugs and kill more cancer cells. Interferon alfa may interfere with the growth of cancer cells. It is not yet known whether giving more than one drug (combination chemotherapy) with radiation therapy and peripheral stem cell transplant is more effective than chemotherapy followed by interferon alfa in treating mantle cell lymphoma.